1. Field of the Invention
The present invention relates to a package for storing a pressure sensor such as a capacitance type pressure sensor.
2. Description of the Related Art
Recently, a capacitance type pressure sensor and a piezo type pressure sensor have been developed to be mounted on various types of the devices. Normally, this type of sensor is required to be packaged with a ceramic package and the like so as to be mounted on the device.
For example, for the purpose of packaging the pressure sensor, an adhesive agent (die bonding agent) is applied over an entire bottom surface of the package, on which the pressure sensor is mounted and adhered (die bonded) on the bottom surface of the package with the adhesive agent, for example as disclosed in Japanese Unexamined Patent Application Publication No. 9-101220.
With this type of process for packaging, the difference in the thermal expansion coefficient between the material for forming the sensor and the material for forming the package may influence the sensor's characteristics. Assuming that the sensor is formed of silicon, which exhibits the thermal expansion coefficient of about 3 to 3.5×106/K, and the package is formed of alumina, which exhibits the thermal expansion coefficient of about 8×106/K, as the thermal expansion coefficient of the material for forming the package is larger, the sensor is adversely affected because of the influence of the thermal expansion of the package. Thus the temperature characteristics of the sensor are deteriorated. Especially in the case where the pressure sensor is sized to have the gap between the substrate and the diaphragm with a ga[ magnitude of several □ms, the resultant thermal expansion may deform the diaphragm, thus failing to accurately detect the pressure.